Device Having a Structured Coating for Use as an Implant, for the Treatment of Eardrum Perforations, and for Cell Cultivation

ABSTRACT

A device having a structured coating for adhering to rough, in particular biological, surfaces, includes a carrier layer, wherein a plurality of protrusions is arranged on the carrier layer, which protrusions each comprise at least a shaft having an end face pointing away from the surface, and wherein a further layer is arranged at least on the end face, wherein the layer has a different modulus of elasticity than the protrusion in question. The further layer can also fill the intermediate spaces between the protrusions such that an internal structured coating is produced.

FIELD OF THE INVENTION

The invention relates to a device having a structured coating, inparticular for adhering to rough, in particular biological surfaces,such as for example eardrums.

Prior Art

Adhesion to rough surfaces is often problematic. In the biological fieldin particular, many adhesives show only unsatisfactory properties. Atthe same time, it is problematic that the surface of the adhesives isonly insufficiently compatible with biological processes such as woundhealing.

An alternative is offered by dry adhesive substances, such as geckostructures, for example, which can also show adhesion to rough surfaceswithout the intermediary of adhesives. However, these substances must beproduced quite frequently and are only adaptable to a limited extent.

Eardrum perforations are a frequently-occurring problem that can lead tohearing loss or frequently recurring infections. Common causes ofeardrum perforations can be middle ear infections, trauma, andpostoperative complications. As a rule, one can distinguish betweenacute (smaller) perforations, which spontaneously close in most cases,and larger or chronic perforations. These larger perforations must besurgically treated by myringoplasty or tympanoplasty, procedures thathave a high success rate, but in addition to the surgical risk, there isalso a risk of residual perforation. In tympanoplasty, moreover,autologous tissue is transplanted, which must be additionally removed.One of the main problems in the regeneration of eardrum injuries is thelack of a carrier layer for the migration of epithelial cells and theformation of a trilayer membrane. As “supporting platforms” one cangenerally use either transplanted tissue or polymers, the function ofwhich can then be improved by using biomolecules. Polymers that can beused for this purpose include gelatin, silk fibroin, chitosan, alginatesor poly(glycerol sebacates). A current survey of results in the use ofthese polymers and various growth factors can be found in the overviewby Hong et al. Although many of the polymers used lead to outstandingresults with respect to closure of the perforation, there aresignificant differences in the morphology of the tissue in question.

Object

The object of the invention is to provide a device having a structuredcoating that shows adhesion in particular to rough surfaces, inparticular biological surfaces, and avoids the drawbacks of prior art.

Means for Achieving Object

This object is achieved by the inventions having the features of theindependent claims. Advantageous improvements of the inventions aredescribed in the dependent claims. The wording of all of the claims ishereby included in the content of this description by reference. Theinventions also comprise all reasonable combinations, and in particularall mentioned combinations of the independent and/or dependent claims.

The object is achieved by means of a device having a structured coating,wherein the device comprises a carrier layer, wherein a plurality ofprotrusions (pillars) is arranged on this carrier layer, whichprotrusions each comprise at least a shaft having an end face facingaway from the surface, characterized in that a further layer is arrangedat least on the end face, wherein this layer has a different elasticmodulus from the protrusion in question.

This further layer also forms the top surface of the device, which isused for adhesion to a surface.

In a perpendicular direction, the device therefore comprises, at theposition of a protrusion, at least two layers starting from the carrierlayer differing in elastic modulus, specifically at least the protrusionand the further layer arranged thereon. This further layer and the endface of a protrusion form an interface between two areas differing inelastic modulus. Depending on the production method, the interfaces canalso comprise thin layers of bonding auxiliaries.

The elastic modulus should preferably be constant within a particulararea.

A protrusion itself can also have further areas differing in elasticmodulus.

The further layer preferably has a lower elastic modulus than theprotrusion on which it is arranged. By means of this structure, theshaft of the protrusion is less elastic than the further layer. Theshaft of the pillar therefore shows less of a tendency towardagglomeration with or without loading. At the same time, the upper partof the protrusion is more elastic and can better adapt itself to roughand/or soft surfaces.

In a further embodiment of the invention, the interface between thefurther layer and the end face is not parallel to the surface of thefurther layer with respect to the respective protrusion.

In an embodiment of the invention, the end face of a protrusion iscurved. Preferably, it comprises a peak within the protrusion. Inparticular, it has a parabolic or hemispherical shape. In this manner,the interface with the further layer also has a corresponding shape.Here, the end face can show a curvature only as far as the edge of theprotrusion, while it has a flat course in the middle of the protrusion.In such an arrangement, the thickness of the further layer above the endface is not constant. If the end face forms a peak in the middle of theprotrusion and the surface of the further layer has a flat shape, thenthe thickness of the further layer decreases above the protrusion towardthe middle of the protrusion.

As a result of such a shape of the interface, materials having differingelasticity or bending stiffness are present and engage with one another.It has been found that such an arrangement increases the adhesive forceof such a protrusion and also decreases its tendency to collapse.

In an embodiment of the invention, the ratio of the minimumperpendicular thickness of the further layer above the protrusion to theheight of the protrusion is less than 3, preferably less than 1, inparticular less than 0.5, and in particular less than 0.2. In thismanner, changes in the thickness of the further layer, e.g. in the caseof curved phase interfaces due to the geometry of the protrusions, havea particularly strong effect on adhesion. The optimum ratio can alsodepend on the ratio of the elastic moduli, as well as the geometry ofthe interface.

In an embodiment of the invention, the curvature of the end face isconvex in the direction of the further layer, i.e. the phase interfacehas a peak. Preferably, the curvature is a spherical curvature, inparticular with a radius of up to twice the diameter of the protrusion,in particular of at least the diameter of the protrusion.

In a further embodiment of the invention, on detachment from a surface,the protrusion begins to detach in the middle. The advantageousparameters for elastic modulus, size ratio and geometry of theinterface, in particular a convex interface, can be determined bysimulations and measurements.

In a preferred embodiment of the invention, the protrusions on thecarrier layer are configured as pillars. This means that these areprotrusions preferably configured perpendicularly to the carrier layerthat have a shaft and an end face, wherein the shaft and the end facemay have any desired section (for example circular, oval, rectangular,quadratic, diamond-shaped, hexagonal, pentagonal, etc.).

Preferably, the protrusions are configured such that the perpendicularprojection of the end face onto the base surface of the protrusion formsan overlapping surface with the base surface, wherein the overlappingsurface and the projection of the overlapping surface onto the end faceform an element on the end face that lies completely inside theprotrusion. In a preferred embodiment of the invention, the overlappingsurface comprises at least 50% of the base surface, preferably at least70% of the base surface, and particularly preferably, the overlappingsurface comprises the entire base surface. The protrusions are thereforepreferably not sloping, but they may be.

In a preferred embodiment, the end face is oriented parallel to the basesurface and to the top surface. If the end faces are not orientedparallel to the top surface and therefore have different perpendicularheights, the average perpendicular height of the end faces is consideredto be the perpendicular height of the protrusion.

In a preferred embodiment of the invention, the shaft of the protrusionhas, with respect to its average diameter, an aspect ratio of height todiameter of 1 to 100, preferably 1 to 10, and particularly preferably 2to 5.

In an embodiment, the aspect ratio is greater than 1, preferably atleast 3, in particular at least 7, preferably 3 to 15, and particularlypreferably 3 to 10.

In this case, the average diameter is understood to refer to thediameter of the circle that has the same area as the correspondingsection of the protrusion, averaged over the entire height of theprotrusion.

In a further embodiment of the invention, the ratio of the height of aprotrusion to its diameter at a specified height over the entire heightof the protrusion is always 1 to 100, preferably 1 to 10, andparticularly preferably 2 to 5. In an embodiment, this aspect ratio isat least 3, in particular at least 7, preferably 3 to 15, particularlypreferably 3 to 10. In this case, diameter is understood to refer to thediameter of a circle having the same area as the corresponding sectionof the protrusion at the specified height.

The protrusions can have widened end faces, so-called “mushroom”structures. It is also possible for the further layer to extend beyondthe end face and thus form a “mushroom” structure.

In a preferred embodiment, the protrusions do not have widened endfaces.

The surface of the further layer can itself be structured so as toincrease its surface. In this case, the average perpendicular height ofthe further layer is taken as the perpendicular thickness of the furtherlayer.

In a preferred embodiment, the perpendicular height of all of theprotrusions is in a range of 1 μm to 10 mm, preferably 1 μm to 5 mm, inparticular 1 μm to 2 mm, and preferably in a range of 10 μm to 2 mm.

In a preferred embodiment, the perpendicular thickness of the furtherlayer above an end face is in a range of 1 μm to 1 mm, preferably 1 μmto 500 μm, in particular 1 μm to 300 μm, preferably in a range of 1 μmto 200 μm, in particular in a range of 10 μm to 200 μm, and mostpreferably 5 μm to 100 μm.

Preferably, the further layer, with respect to at least 50% of theprojection of the base surface of a protrusion onto the surface of thefurther layer, has a perpendicular thickness in the above range or oneof the preferred ranges.

The smallest thickness of the further layer above a protrusion ispreferably always less than the maximum perpendicular height of theprotrusion.

In a preferred embodiment, the perpendicular thickness of the carrierlayer is in a range of 1 μm to 2 mm, preferably 1 μm to 500 μm, and inparticular 1 μm to 300 μm.

In a preferred embodiment, the base surface, in terms of its area,corresponds to a circle with a diameter of between 0.1 μm and 5 mm,preferably 0.1 μm and 2 mm, particularly preferably between 1 μm and 500μm, and particularly preferably between 1 μm and 100 μm. In anembodiment, the base surface is a circle with a diameter of between 0.3μm and 2 mm, preferably 1 μm and 100 μm.

The average diameter of the shafts is preferably between 0.1 μm to 5 mm,preferably 0.1 μm and 2 mm, and particularly preferably between 1 μm and100 μm. Preferably, the height and the average diameter are adaptedaccording to the preferred aspect ratio.

In a preferred embodiment with widened end faces, the surface of the endface of a protrusion, or the surface of the further layer, is at least1.01 times, preferably at least 1.5 times larger than the area of thebase surface of a protrusion. For example, it can be larger by a factorof 1.01 to 20.

In a further embodiment, the widened end face is between 5% and 100%larger than the base surface, particularly preferably between 10% and50% of the base surface.

In a preferred embodiment, the distance between two protrusions is lessthan 2 mm, in particular less than 1 mm, and most preferably less than500 μm or less than 100 μm.

The protrusions are preferably regularly arranged at periodic intervals.

In a preferred embodiment of the invention, the protrusions have aheight of 5 to 50 μm, and preferably up to 25 μm. The further layer hasa perpendicular thickness above the end faces of 3 to 70 μm. The averagedistance between the pillar-shaped protrusions is between 5 and 50 μm.The thickness of the carrier layer is between 5 and 100 μm. Depending onthe distance between the protrusions, the diameter is 5 to 40 μm.Preferably, the protrusions are hexagonally arranged. Particularlypreferably, the density of the protrusions is 10,000 to 1,000,000protrusions/cm².

The total thickness of the device, comprising the further layer, theprotrusions, and the carrier layer, is preferably between 50 μm and 300μm.

The elastic moduli of all areas of the protrusion and the further layerare preferably 50 kPa to 3 GPa. Preferably, the elastic modulus of softareas, i.e. in particular the further layer, is 50 kPa to 20 MPa,preferably 100 kPa to 10 MPa. Independently of this, the elastic modulusof the areas with a high elastic modulus, e.g. the protrusions and e.g.the carrier layer, is preferably 1 MPa to 3 GPa, and more preferably 2MPa to 1 GPa. Preferably, the elastic moduli of all softer and harderareas are in the ranges given above.

The ratio of the elastic moduli between the lowest elastic modulus andthe area with the highest elastic modulus is preferably less than1:2000, in particular less than 1:1500, preferably less than 1:1200,independently thereof at least 1:1.1, preferably at least 1:1.5, and inparticular at least 1:2. In this case, a ratio of up to 1:1000 can beadvantageous. Preferably, the further layer has the lowest elasticmodulus. In particular, the ratio is 1:1.1 to 1:500, and preferably 1:2to 1:500.

In a further embodiment of the invention, the ratio of the elasticmoduli of the area of the device with the lowest elastic modulus and thearea with the highest elastic modulus is preferably 1:2 to 1:200 (softto hard), and in particular 1:2 to 1:100.

In a further embodiment, the ratios indicated above describe the ratioof the elastic modulus of the further layer (soft) to that of theprotrusions (hard).

In a particularly preferred embodiment of the invention, the furtherlayer additionally fills the intermediate spaces between theprotrusions.

In this embodiment, the device can be seen as a coating composed of atleast two components, wherein these two components have a structuredinterface between them because of the protrusions now embedded in thecoating. The upper side of the further layer preferably has a planarshape, and the underside of the carrier layer also preferably has such ashape. The indications given on the thickness of the further layer referto the part of the further layer arranged above the end faces.

The protrusions are additionally stabilized by filling of theintermediate spaces. It was surprisingly found that such layers alsoshow increased adhesion. The enclosed protrusions are also stabilized bythe material surrounding them. Because of this, tensile forces parallelto the contact surface of the device do not cause collapsing of theprotrusions, but the adhesive force remains present even in the event ofsuch tensile forces. This is important for example if, in addition toadhesion, the device is also intended to withstand tensile forcesparallel to the contact surface. An example of this is application onwounds to be closed or injuries of the eardrums.

Moreover, this layer can easily be kept clean or sterile, as nocontamination whatsoever can accumulate in the intermediate spaces.

Additionally, the filled structure makes it possible to reduce stresspeaks that may occur in the case of freestanding protrusions ondetachment from a surface.

In addition, such a device can more easily be produced, as one needsimply coat the carrying layer having the protrusions with the materialof the further layer. Complex structuring steps are not required.

The surface of the device in this embodiment appears closed and uniform.This allows it to be more easily modified for adaptation to particularapplications. In this case, treatment of the surface does not affectstructuring inside the coating.

The surface can thus be functionalized or treated using known methods.

In a further embodiment of the invention, the further layer part is afilm that connects the protrusions. In this case, the intermediatespaces between the protrusions are not filled.

The film preferably has a thickness that is less than 100%, preferablyless than 50%, and particularly preferably less than 30% of theperpendicular height of the bridged protrusions. In this case, the filmis not included in calculation of the height.

The film preferably has a thickness of less than 2 mm, preferably lessthan 1 mm, and particularly preferably less than 800 μm.

The protrusions may be composed of many different materials, and arepreferably elastomers, particularly preferably crosslinkable elastomers.The areas with a higher elastic modulus can also comprise duroplasts.

The protrusions and the further layer can therefore comprise thefollowing materials:

Epoxy- and/or silicone-based elastomers, polyurethanes, epoxy resins,acrylate systems, methacrylate systems, polyacrylates as homo- andcopolymers, polymethacrylates as homo- and copolymers (PMMA, AMMAacrylonitrile/methyl methacrylate), polyurethane(meth)acrylates,silicones, silicone resins, rubbers such as R rubber (NR natural rubber,IR polyisoprene rubber, BR butadiene rubber, SBR styrene-butadienerubber, CR chloropropene rubber, NBR nitrile rubber, M rubber (EPMethene-propene rubber, EPDM ethylene-propylene rubber), unsaturatedpolyester resins, formaldehyde resins, vinyl ester resins, polyethylenesas homo- or copolymers, and mixtures and copolymers of theabove-mentioned materials. Also preferred are elastomers approved foruse in the field of packaging, medicinal products and food products bythe EU (according to EU Regulation No. 10/2011 of 14 Jan. 2011 publishedon 15 Jan. 2011) or the FDA or silicone-free UV curable resins from PVDand CVD process engineering. In this case, polyurethane(meth)acrylatesstands for polyurethane methacrylates, polyurethane acrylates, andmixtures and/or copolymers thereof.

Hydrogels, for example based on polyurethanes, polyvinylpyrrolidone,polyethylene oxide, poly(2-acrylamido-2-methyl-1-propanesulfonic acid),silicones, polyacrylamides, hydroxylated polymethacrylates or starchescan also be used.

Epoxy- and/or silicone-based elastomers, polyurethane(meth)acrylates,polyurethanes, silicones, silicone resins (such as UV-curable PDMS),polyurethane(meth)acrylates, and rubber (such as EPM, EPDM) arepreferred.

Particularly preferred are crosslinkable silicones, such as for examplepolymers based on vinyl-terminated silicones.

Among the above-mentioned substances, for the further layer that is incontact with the surface, the epoxy- and/or silicone-based elastomers,polyurethane(meth)acrylates, polyurethanes, silicones, silicone resins(such as UV-curable PDMS), polyurethane(meth)acrylates, and rubber (suchas EPM, EPDM), in particular crosslinkable silicones, such as forexample polymers based on vinyl-terminated silicones, are particularlypreferred.

The above-mentioned hydrogels or pressure-sensitive adhesives can alsobe used for the further layer.

In a further embodiment, the surface of the further layer is treated.This allows the properties of the surface to be influenced. This cantake place by means of physical treatment such as plasma treatment,preferably with Ar/O₂ plasma.

Covalent or non-covalent bonds to additives on the surface can also beformed, for example in order to achieve a certain compatibility with thecells. Preferred are additives for supporting cell adhesion, such ase.g. poly-L-lysine, poly-L-ornithine, collagen, or fibronectin. Suchadditives are known from the field of cell culturing.

In application in the medical field in particular, it can beadvantageous to store substances in one part of the device which arethen slowly released. For example, these can be drugs such asantibiotics, or adjuvants for supporting cell adhesion or cell growth.

In a further embodiment, the protrusions and the carrier layer areconfigured as a single piece and are composed of the same material.

In a further embodiment, the device also comprises further layers, whichcan optionally be detachable. In this manner, the surfaces can beprotected prior to use by detachable films. Further stabilizing layerscan also be arranged on the carrier layer.

The carrier layer preferably has a thickness that is less than themaximum height of the protrusions arranged on it.

As the carrier layer, if it is composed of the same material as theprotrusions, comprises a material having a higher elastic modulus, thethickness of the carrier layer can also be used to influence theelasticity of the entire device.

The device according to the invention is preferably configured foradhering to soft substrates.

The device according to the invention is configured in particular foradhering to biological tissues. For this purpose, it can be configuredfor example as a film. It can also be configured in combination with thedevices to be secured in place. For example, these can be dressingmaterial, but also electrodes or other medical devices such as implants,in particular implants that are not to be anchored on bones, or softimplants. For example, these can be iris implants. The inventiontherefore also relates to an implant comprising a device according tothe invention, for example on at least a portion of the surface of theimplant.

The invention further relates to use of an above-mentioned device foradhering to biological tissues. These can be any desired tissues, suchas skin, but also internal tissues such as organ surfaces, woundsurfaces, or eardrums. The device allows the combination of awell-tolerated surface with simultaneous adhesion to the biologicaltissue. The device therefore also serves as a growth substrate for thecell cultivation or for the new tissue to be formed.

Treatment of Eardrum Perforations

Because of its adhesion, the device adheres quite favorably to thesurface of the eardrum, and even makes it possible to apply it understress. Because of its structure, it adheres to the surrounding tissuesand not only to the eardrum. Optionally, the device configured in thismanner can comprise different areas having different adhesion. This cantake place via the material or the layer thickness of the further layer,but also simply by distribution of the protrusions within the device.

The device, which is advantageously configured as a film, thereforecomprises at least the carrier layer with the protrusions, and thefurther layer is applied to these protrusions in such a way that theintermediate spaces are filled. By means of the embodiment as a film,the device can easily be cut to the desired size. This can even be donepersonally by the person carrying out treatment, e.g. the physician.

Because of its structuring, the device adheres favorably to the tissueto which it is applied. In addition to the eardrum, this can also be thesurrounding tissue. No liquid component, which could flow into the ear,is required for application of the device.

Depending on the material used, the device can also be transparent, suchthat the status of the tissue under the device can be observed, forexample in order to confirm healing, without detaching the device. Thedevice is preferably transparent.

Because of its dry adhesiveness, the device can easily be re-detached.

Surprisingly, it was also found that the devices according to theinvention, in particular the device in which the further layer fills theintermediate spaces, show advantageous properties for cell cultivation,i.e. the cultivation of cells outside of an organism. The can easily becut to size. Because of the E modulus of the two layers, in particularof the further layer, on which the cells are cultivated, the device canbe adapted to the cells to be cultivated (E modulus (brain cells):approx. 0.1-1 kPa; E modulus (muscle cells): approx. 8-17 kPa; E modulus(bone cells): approx. 25-40 kPa).

In particular, the device can be easily divided after cultivation of thecells so that various tests can be conducted based on the same cellculture. As the device can be transparent, the cultures obtained in thismanner are also suitable for microscopic tests. For example, they can becut using razor blades or a scalpel. The device can also be applied tocommon glass supports, e.g. round glass slides.

Alternatively, the device can also be used directly for cultivation incorresponding cultivation receptacles.

The surface of the device can also be physically or chemically treatedfor cultivation. This can be done for example by autoclaving, forexample by steam sterilization at 50 to 200° C., in particular 100 to150° C., at a pressure of 1 to 5 bar for 5 min to 3 h. In suchautoclaving (121° C., 2 bar, 20 min), no significant change in adhesivestress was observed.

For example, the surface can be treated with poly-L-lysine,poly-L-ornithine, collagen, fibronectin, gelatin, laminins, keratin,tenascin or perlecan. Such additives are known from the field of cellculturing.

The invention also relates to a method for producing an embodiment ofthe device according to the invention.

Individual method steps will be described in further detail in thefollowing. The steps do not necessarily have to be carried out in theorder indicated, and the method to be described can also have furthersteps not mentioned here.

For this purpose, in a first step, a template is provided for moldingthe plurality of protrusions.

The material for the protrusions is introduced into this template,preferably as a liquid. Optionally, the material can also already be atleast partially cured.

After this, the material for the carrier layer, i.e. the surface onwhich the protrusions are arranged, is applied to the template andcured. Particularly preferably, this is the same material as for theshafts of the protrusions, so that the carrier layer and the shafts canalso be produced in one step, for example by directly introducing alarger amount of material.

In a next step, the carrier layer and the protrusions are detached fromthe template.

After this, the material for the further layer is applied to the surfacewith the protrusions in an amount such that the protrusions arecompletely covered. This can be carried out for example by doctoring orspin coating.

In a next step, the further layer is cured.

Further details and features will be found in the following descriptionof preferred examples in connection with the dependent claims. In thiscase, the respective features can be implemented individually or asmultiple features in combination with one another. The possibilities forachieving the object are not limited to the examples. For example, inall cases, ranges given include-unspecified-intermediate values and allconceivable partial intervals.

The examples are shown schematically in the figures. The same referencenumbers in the individual figures denote the elements that areidentical, functionally identical, or correspond to one another withrespect to their functions. More specifically, the figures show thefollowing:

FIG. 1 A schematic view of a section of an embodiment of the invention;

FIG. 2 SEM images of layers according to the invention; produced by spincoating of SSA 50:50 on a microstructured PDMS layer at 6000 rpm; thePDMS layer was produced with weights (100 g);

FIG. 3 Dependency of the layer thickness over the microstructured PDMSlayer on spin coating velocity; all PDMS layers were produced withweights (100 g);

FIG. 4 A statistical evaluation of the obtained layer thicknessdepending on the use of weights;

FIG. 5 An SEM image of a section through a layer of SSA 50:50 applied byspin coating to a glass substrate;

FIG. 6 Dependency of the layer thickness of SSA 50:50 on a glass surfaceon spin coating velocity;

FIG. 7 Adhesion force of SSA and PDMS in various ratios against a smoothsubstrate (SMOOTH) in various applications; (A: pull-off stress vs.velocity; B: pull-off stress vs. layer thickness; C: maximum strain vs.layer thickness; D: adhesion energy vs. layer thickness; layer thicknesswas determined by SEM;

FIG. 8 Micrographs of L929 cells 4 h after plating on PDMS (A, C, E, G)or SSA 50:50 (B, D, F); unmodified (A and B); modified withpoly-L-lysine (C and D); poly-L-ornithine and subsequent incubation withfibronectin (E and F); G cells cultivated on tissue-culture-treated(TC-treated) polystyrene;

FIG. 9 Micrographs of L929 cells after 24 h on PDMS (A), SSA 50:50 (B),and treated respectively with O₂/Ar plasma-treated PDMS (C) or SSA 50:50(D);

FIG. 10 Cell number after 24 h on the surfaces according to FIG. 9starting from 3×10³ vital cells (student's t test, * p<0.05 **p<0.0005);

FIG. 11 Activity (in percent of cytotoxicity) of lactate dehydrogenase(LDH) after 24 h cultivation on the surfaces according to FIG. 9 and acontrol;

FIG. 12 Comparison of the adhesion force of structured coatings(PDMS/SSA 50:50; 20 μm layer thickness SSA 50:50 over the protrusions)and unstructured coating PDMS/SSA 50:50;

FIG. 13 Tensile force tests with unstructured coatings of Vitro-Skin®(structure shown in A); B shows the measured tensile forces for PDMS(reference) and PDMS, to which SSA was applied in various mixing ratiosfrom 40:60 to 52:48;

FIG. 14 Micrographs of L929 cells after 48 h on PDMS (A), SSA 50:50 (B),PDMS with PLL (C), SSA 50:50 with PLL (D); images A1, B1, C1 and D1 showthe samples after shaking for 60 s;

FIG. 15 Contact angle for various surfaces before and after plasmatreatment (left to right: PDMS; PDMS plasma; SSA 40:60; SSA 40:60plasma; SSA 50:50; SSA 50:50 plasma);

FIG. 16 The complex modulus of SSA 40:60 and SSA 50:50 was determined byrheometry at frequencies of between 0.1 and 100 Hz. The measurementamplitude was 0.1%;

FIG. 17 Comparison of various adhesion parameters between roughsubstrate and smooth substrate: (A) determination of pull-off stressdepending on holding time after the substrate was pressed onto thepreparations with a force of approximately 40 mN. The thickness of thepreparations, which was tested using rough substrate, was between 130 μmand 170 μm. (B) Comparison of pull-off stress in use of a roughsubstrate and a smooth substrate. (C) Determination of the maximumstrain using a rough substrate and a smooth substrate. (D) Determinationof adhesion energy in use of a rough substrate and a smooth substrate.

FIG. 18 Schematic structure of the measuring apparatus used to determineadhesion values (A). Determination of the roughness of the glasssubstrate used for the measurements. The curve (distance vs. height) forthe smooth substrate shows virtually no deviations in contrast to therough substrate.

FIG. 19 Schematic view of the production process;

FIG. 20 Schematic view of sections of further embodiments of theinvention.

Soft Skin Adhesive (SSA) from Dow Corning was used for the tests. Theseare vinyl-terminated silicones. By mixing two solutions, A and B, curingof the polymers is catalyzed and Pt is initiated. The tests were carriedout with MG 7-9800. The compositions used are indicated in SSA A:B.

FIG. 1 shows a schematic view of a section of an embodiment of theinvention. The device comprises a carrier layer (100) on which aplurality of protrusions (110) is arranged. A further layer (120) isarranged on the end face (140) of the respective protrusions. In thiscase, this layer also fills the intermediate spaces (130) between theprotrusions. The surface (150) of the further layer is the surface usedfor adhesion. The protrusions themselves preferably have a circularsection and therefore constitute pillars.

FIG. 2 shows SEM images (SEM: scanning electron microscope) that showthe effect of increasing centrifugal acceleration in the production ofthe SSA layer on a microstructured PDMS surface.

The decrease in layer thickness with increasing revolution speed can beclearly seen.

FIG. 3 shows the layer thicknesses as determined by SEM at differentvelocities (for 90 s respectively). In this case, the layer thickness istaken to be the thickness of the layer over the microstructured PDMSsurface.

FIG. 4 shows the effect of weights on the layer thickness of theproduced PDMS carrier layer (also see FIG. 19, upper method). By placingweights on the layer, thinner layers can be obtained. This allows moreflexible devices to be obtained.

FIG. 5 shows an SEM image of an SSA 50:50 layer on glass. In this caseas well, the layer thickness can be set via the conditions during spincoating. The corresponding layer thicknesses obtained are shown in FIG.6. The time was 90 s in all cases. However, similar layers can also beobtained at lower velocity and with a longer duration.

FIG. 7 shows the values for measurement according to FIG. 18 in variousapplied layers. PDMS (Slygard 184) was used. The ratio indicates theproportions of PDMS and the crosslinker.

Various layer thicknesses (50 μm to 250 μm) were applied to a glasssurface by means of the doctoring method. Increasing adhesion wasmeasured with decreasing layer thickness. It can be seen for all of thematerials that an increase in pull-off speed leads to higher adhesivestresses (FIG. A). There is a pronounced dependency between filmthickness and all of the tested parameters for all of the SSA mixtures.These parameters include pull-off stress (FIG. B), maximum strain (FIG.C), and adhesion energy (FIG. D). Because of the considerably greater Emodulus of PDMS, there is substantially less dependency of pull-offstress on film thickness in this case. It can be seen from FIG. B inparticular that the pull-off stress depends on the E modulus of thematerials. The stiffer the material, the higher the stresses observed.One notes on observation of maximum strain (FIG. C) that the maximumstrain of SSA 50:50 is significantly greater than that of all the othermaterials tested.

FIG. 8 shows the effect of surface modification on the adhesion of L929cells (fibroblasts, species mice). For this purpose, such cells weremicroscopically examined on the respective surfaces after a plating timeof 4 h. For PDMS and SSA 50:50, minimal cell adhesion is seen when thesurfaces are not modified (A and B). Adsorption of poly-L-lysine to thesurface resulted in a clear increase in the adhesion behavior and theformation of cellular extensions for PDMS (C) and SSA 50:50 (D).

It was possible to significantly improve this adhesion behavior bytreatment of the polymer surface with poly-L-ornithine and subsequentincubation with fibronectin for PDMS (E) and SSA 50:50 (F). In thiscase, the flattened cellular morphology is comparable to that ofcell-culture-treated polystyrene. The adhesion properties of the SSA50:50 were retained after the surface modification.

Poly-L-ornithine and poly-L-lysine solutions were incubated for 20 minat 37° C. on the polymer surface; they were then rinsed with phosphatebuffer (PBS). Bovine fibronectin was incubated for 60 min at 37° C. Theconcentration was 10 μg/ml PBS. After this, PBS washing and air-dryingwere carried out.

The adhesion behavior of L929 cells on PDMS and SSA 50:50 after acultivation time of 24 h was also investigated. For this purpose, 3×10³vital cells were cultivated for 24 h on PDMS (A), SSA 50:50 (B),plasma-treated PDMS (C), and SSA 50:50 (D) (FIG. 9). After this periodof time, the cells were enzymatically removed from the surface and thecell number was determined (FIG. 10). In order to test for a cytotoxiceffect of cultivation on PDMS or SSA 50:50, lactate dehydrogenase (LDH)activity after 24 h of cultivation was investigated (FIG. 11). Nocytotoxic effect was observed under any of the conditions. The effect ofplasma treatment on the contact angle of the surface is shown in FIG.15.

FIG. 12 shows the effect of structuring. Microstructured surfaces thatwere coated with SSA 50:50 affect the adhesion force. SSA 50:50 wasapplied by spin-coating to a microstructured PDMS layer with pillarheights of 20 μm. The adhesion force of the coated pillar structures issignificantly higher in areas in which no protrusions are present. Themeasurement was carried out on the same sample, which had structured andunstructured areas.

FIG. 13 shows the structure for tensile force tests with unstructuredtwo-layer composites against Vitro-Skin®. For this purpose, a two-layercomposite composed of a PDMS layer to which the SSA was applied inmixing ratios of 40:60 to 52:48 was produced. A preparation composed ofPDMS was used as a reference. FIG. 13 A shows an example of thestructure of the test. Vitro-Skin® is a synthetic material thatsimulates the surface properties of human skin (roughness R_(a)=12-15μm). PDMS and SSA in a mixing ratio of 40:60 showed no adhesionwhatsoever. Maximum adhesion was obtained with SSA in the mixing ratiosof 50:50 and 52:48 (FIG. 13 B).

The adhesion force of L929 cells on the surfaces was also tested. FIG.14 shows corresponding light micrographs. L929 cells were plated for 48h on PDMS (A) and SSA 50:50 (B). The average layer thickness was between130 μm and 200 μm and was determined using an optical system.

In addition, the surface of the polymers was functionalized by applying0.01% poly-L-lysine (PLL) (PDMS (C) and SSA 50:50 (D)). The cells wereplated as individual cells. Generally speaking, one cannot observe anydifference microscopically in quantitative cell adhesion between PDMSand SSA, as the cells form extensions on both materials (arrows on theimages). On SSA, the cells generally appear to be flatter and moreelongated. The same impression can be seen on the PLL coated surfaces(C, D). In order to investigate how the cells behave under mechanicalstress, all of the samples were shaken with the same force for a periodof approximately 60 s. This leads to significant detachment of the cellsfrom the PDMS surface (A1). The aggregates in this image are no longerin contact with the polymer surface (arrows in in A1). In comparison tothis, on the SSA surface one finds a sharp reduction in the cellularextensions compared to A, but no detachment of the surface occurs (B1).The functionalization by means of PLL clearly prevents detachment of thecells on the PDMS surface (C1) and prevents the reduction of the cellextensions on SSA (D1). Nevertheless, the cells appear to be more“spherical” than in FIG. D. This morphology appears to be typical forcells with low adhesion contacts to the surface. In summary, one can sayhere that the cells on the SSA surface are less sensitive to mechanicalstress. Cellular adhesion can be significantly improved by a surfacemodification, as shown in D1.

SSA 50:50-PDMS composite structures were produced and applied to theintact eardrum of a dead mouse. The composite structure was cut to therequired dimensions and then applied with the adhering side to theintact eardrum. Repeated detachment and repositioning did not cause theeardrum to rupture. In a further step, a part of the eardrum was cutopen in order to simulate a rupture. It was possible to fasten thecomposite structure to the edges of the wound and exert a lateral pull.

The complex modulus of SSA 40:60 and SSA 50:50 was determined byrheometry at frequencies of between 0.1 and 100 Hz (FIG. 16). Themeasurement amplitude was 0.1%. The results show that SSA 50:50 has alower E modulus than SSA 40:60. The approximate ratios were a ratio ofabout 6 between PDMS 10:1 and SSA 40:60 and a ratio of about 65 betweenPDMS 10:1 and SSA 50:50.

A comparison of the two substrates to each other shows that the pull-offstress of SSA in use of a rough substrate (glass R_(a)=0.271 μm) ishigher than for PDMS (FIG. 17). SSA 50:50 shows comparable pull-offstresses when a rough or smooth substrate (R_(a)=0.006 μm) is used (A,B). The maximum strain of SSA 50:50 is substantially higher for SSA50:50 than for PDMS (C). The adhesion energy of PDMS is substantiallylower in use of a rough substrate than the adhesion energy of SSA 40:60and SSA 50:50 (D).

This shows that the structured coatings according to the invention arebetter suited for rough surfaces, i.e. surfaces having a roughness ofgreater than 0.2 μm. For a mouse eardrum, a roughness of approximatelyR_(a)=1 μm was measured after vapor deposition of a thin gold film.

FIG. 18 A shows a schematic view of the measuring apparatus fordetermination of the measurement values. The structured coating (polymerfilm) is pressed against a substrate (glass substrate) using a moveable(pivotable) table. Both the pressing force and the adhesion force on thesubstrate when the structured coating is moved away can be measuredusing a load cell. B shows measurement of the roughness of the glasssubstrate used for the measurements (roughness measured in all cases bywhite light interferometry).

FIG. 19 shows the production process. In (1), a structured surface isfirst produced, which in (2) is then further processed into a structuredcoating with a further layer. From left to right, (1) shows theapplication of the first polymer (prepolymer 1) either to a glass slideor a microstructured MD40 master (hexagonally arranged pillar-shapedprotrusions with a diameter of 7 μm, a height of 18 μm, and acenter-to-center distance of 14 μm) located on a glass slide. New PDMSis applied to the MD40 master, air is withdrawn in a vacuum, and aplasma-activated glass slide is applied to the surface. Weights areapplied to this (e.g. 10 g/cm²), which makes it possible to influencethe thickness of the PDMS layer, which constitutes the carrier layer forthe protrusions (e.g. 40±9 μm). After polymerization at 95° C. to 100°C. for one hour, the MD40 mold can be removed. (2) The second polymer(prepolymer 2, e.g. SSA) can now be applied by the spin-coating methodto the microstructured PDMS layer, which is also treated with plasma.The composite structure produced in this manner is polymerized at 95° C.to 100° C. After this, the surface can also be functionalized forbiological applications. This method was used to produce both structuredcoatings and unstructured coatings as comparison samples. The parametert denotes the thickness of the further layer above the protrusions,while b denotes the thickness of the carrier layer.

FIG. 20 shows a section of further embodiments of the invention. Theprotrusions need not have a rectangular shape in a longitudinal section.It is also possible for the end faces of the protrusions to be curved,in particular convex with respect to the further layer (FIG. 20, top).

A further embodiment of the invention is shown at bottom in FIG. 20.Here, the interface between the protrusions and further layer is a wavyline. The protrusions therefore have the three-dimensional form of aparaboloid of revolution.

It is important for all of the variants that there be a sufficientlylarge area of the further layer in which the perpendicular thickness ofthe further layer is in accordance with the ratio according to theinvention with respect to the height of the protrusions in said area. Inthese areas with a thinner further layer, advantageous adhesionproperties are formed. By avoiding edges in the shape of theprotrusions, in particular at their end faces, one can avoid stresspeaks on detachment of the device from a surface, which improvesadhesion.

REFERENCE NUMBERS

-   100 Carrier layer-   110 Protrusion-   120 Further layer-   130 Filled intermediate space-   140 End face-   150 Surface facing the surface of substrate

1. A device having a structured coating, wherein the device comprises: a carrier layer, wherein a plurality of protrusions is arranged on this carrier layer, which protrusions each comprise at least a shaft having an end face pointing away from a surface of the carrier layer, and a further layer arranged at least on the end face, wherein this further layer has a different elastic modulus than the protrusion in question.
 2. The device as claimed in claim 1, wherein the further layer arranged on the end face has a lower elastic modulus than the respective protrusion.
 3. The device as claimed in claim 1, wherein the protrusions have an aspect ratio of greater than
 1. 4. The device as claimed in claim 1, wherein the protrusions have an aspect ratio of at least
 3. 5. The device as claimed in claim 1, wherein the further layer additionally fills the intermediate spaces between the protrusions.
 6. The device as claimed in claim 1, wherein the further layer is part of a film that connects the protrusions.
 7. The device as claimed in claim 1, wherein the device is configured for adhering to soft substrates.
 8. The device as claimed in claim 1, wherein the device is configured for adhering to biological tissues. 9-10. (canceled)
 11. An implant comprising a device as claimed in claim
 1. 12. A method for treating eardrum perforations, comprising: providing a device as claimed in claim 1; and applying the device to a surface of an eardrum having a perforation.
 13. A method for cultivating cells, comprising: cultivating cells on the device as claimed in claim 1; and cutting the device to a desired size. 